Brake booster



W. STELZER BRAKE BOOSTER July 30, 1946.

Filed Deo. 23, 1943 IN V EN TOR.

Patented July 30, 1946 UNITED STATES PATENT OFFICE BRAKE BOOSTER William Stelzer, East Orange, N. J.

Application December 23, 1943, serial No. 515,328

(o1. cli-54.5)

9 Claims.

The invention relates to brake boosters and .more particularly to improved power operated boosters of the compound type to boost the pressure in hydraulic braking systems.

The object of the invention is to provide a pair of boosters, one of which is intended to operate at low pressures while the slack of the brakes is taken up, and the other to take over when the brake shoes are in contact with the drums, -being capable to multiply the hydraulic pressure generated by the master cylinder to obtain a maximum braking eiTort.

Another object is to proportion the boosters so that the low pressure booster transmits a comparatively large volume of hydraulic fluid at low pressure, and the high pressure booster transmits a comparatively small volume of hydraulic iluid at high pressure, the purpose of this arrangement being to save power and to produce a construction which is capable of high capacity and yet may be reduced in size.

Other objects and advantages of this invention Will be apparent from the following description considered in connection with the accompanying drawing submitted for the purpose of illustration and not to define the scope of the invention, reference being had for that purpose to the subjoined claims. In the drawing, wherein similar reference characters refer to similar parts throughout the several Views:

The gure is a cross-sectional side elevation of the boosters, the rest of the hydraulic braking system being illustrated diagrammatically.

Before explaining the present invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawing, since the invention is capable of other embodiments and of being practised or carried out in various ways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not limitation.

Describing the invention now in detail, and referring to the figure, there is shown a conventional master cylinder I operated by the oper ator by means of brake pedal 2 pivoted at 3. A hydraulic brake line 4 leads from the master cylinder to the boosters which in the embodiment shown are combined into a single structural unit comprising a primary pressure cylinder 5 and coaxial secondary pressure cylinders 6 and 1 with expansi-ble chamber motor mechanisms interposed. Excepting the proportion between the hydrauliccylinders and the'expansible chamber motor mechanisms, both boosters are alike, so that the description of one automatically also applies to the other. The description refers to the low pressure booster which is the one that is in operation while the shoes expand to contact the brake drums, corresponding parts belonging to the high pressure booster being identin fied with a prime Both boosters have the primary pressure cylinder `.i in common, or it may be considered that the primary cylinders of both boosters are joined together. Within cylinder 5 slides a control piston 8 provided with a seal v9 and extending into the secondary pressure cylinder in which slides a power piston I0 having a central bore I I in which piston 8 is adapted to slide a short distance. The expansible chamber motor mechanism intermediate cylinders 5 and 6 comprises a circular ange or shell I2 extending from cylinder 5, a circular shell or housing I3 extending from cylinder 6, with a diaphragm I4 interposed dividing the motor mechanism into a Working chamber I5 and a vacuum or reservoir chamber I6, the latter being connected through line II to a source of suction such as the intake manifold IB of an internal combustion engine. The central portion of diaphragm I4 is secured to the diaphragm plate I9 which extends outwardly from piston IU and houses follow-up valves 20 and 2l engaged by a valve actuating plate 22 having a central hole to nt freely over the smaller part of piston 8 whereby the latter engages the plate at 23. Valve 20 serves to control the communication between chambers I5 and I6 through passages f 24 and 25, being held open -by means of spring 26. Valve 2I is ordinarily held in a closed position by spring 2l and controls the admission of air from a source of pressure 23, such as the atmosphere, through line 29, flexible hose 30, and passage 3l to chamber I5. Piston I0 is provided with a seal 32 which also serves to seal the small end of control rod 8 extending into chamber `33 of cylinder 6. The seal is retained by a retainer 34 pinned to piston 8 with a pin 35 pre venting check valve ball 36 from falling out of bore 3l which houses it. Piston 8 has a central hole 38 in which is placed a single rod 39 serving both boosters and extending from ball 36 to ball 36', keeping both of them unseated when the boosters are in the retracted or starting position, as shown.

Chamber 33 is in communication with the wheel cylinders 40 through line 4I, where a check valve 42 is interposed, allowing fluid to flow from chamber `33 to thev wheel cylinders 3 but not vice versa. A pin 43 serves to retain ball 42. Cylinder 'I is not provided with a check valve. Spring 44 urges the pistons into the retracted position.

As indicated on the drawing, the motor mechanism of the low pressure booster is smaller than that of the high pressure booster. It is apparent that a similar proportion would -be maintained between cylinders and motor mechanism if both motor mechanisms were of the same size but the hydraulic cylinders of the low pressure booster were larger and those of the high pressure booster were smaller. In order that the low pressure booster goes into operation before the high pressure booster, it is necessary that spring 21' is stronger than spring 2l. By studying `the operation of the boosters it will become apparent draulic fluid is forced from both chambers, 33 and 33', to the wheel cylinders. Since th'e motor mechanism of the low pressure booster is 0f relatively small size, a condition is soon reached where full atmospheric pressure exists in chamber I5 and the pressure cannot be further in creased so that pistons 8 and I0 stop and ball l2 becomes seated because the flow of iluid from chamber 33 to wheel cylinders 4B has ceased. However, the high pressure booster at the left continues to operate so that the hydraulic pressure in chamber 33 is further increased to obtain a maximum braking effort commensurate with the pedal pressure. Ball 42 prevents the fluid under higher pressure to back up into cham- 'g ber 33.

that the retraction of pisto-n III from the extended position occurs solely by virtue'of spring 44. Therefore, I prefer to make the bore of chamber 33 slightly larger than that of chamber 45, thereby the existing hydraulic pressure assists in returning the pistons, as soon as the motor mechanism is deenergized.

In operation, the booster is in the released or starting position when the brakes are released, as shown. Supposing new that the operator depresses the brake pedal, the hydraulic pressure produced by master cylinder I is transmitted through hydraulic line 4 to chamber 45, and from there through passages 32 and 38', chambers 33 and 33', and lines 4I and 4I to wheel cylinders 43 to actuate the brakes. The hydraulic pressure in chamber 45 acting on piston 8 moves the latter towards the right against the opposition of the hydraulic pressure in chamber 33 acting on the small end of piston 3. Piston 8 actuates plate 22. Spring 26 being weaker than 2l', it yields first, so that valve becomes seated, whereby plate 22 pivots on ball 2| and is contacted by shoulder 23 only at its lower portion. After ball 29 is seated it becomes the pivot point for plate 22 and further movement of piston S causes ball 2I to unseat so that air is permitted to enter from 28 into chamber I5 to urge diaphragm I4 and pistons I9 and I towards the right in unison with piston 8. This movement permits the seating of valves 36 and 35' whereby the hydraulic pressure in chambers 33 and 33 may now be increased to a predetermined multiple of the master cylinder pressure. The ratio between the primary or master cylinder pressure and the secondary or boosted pressure depends on the proportion of the area of piston 3 subject to the hydraulic pressure in chamber 45 and the r smaller area responsive to the hydraulic pressure in chamber 33. Thus as soon as the pressure in chamber 33 exceeds a certain multiple of the pressure produced by master cylinder I, the movement of piston 8 is retarded so that valve 2| is permitted to close to stop the fiow of air to chamber I5. As pistons S and I I) enter into cylinder 6, the fluid displaced in chamber 33 is forced to wheel cylinders 4I) to force the brake shoes against the brake drums. After the shoes are in contact with the drums and brake pedal 2 is further depressed, the hydraulic pressure increases, not only in the wheel cylinders but also in master cylinder l. Due to the increased pressure which urges piston 8' towards the left, rst spring 25 and then 21 yields so that communication between chambers I5 and I6 is interrupted and air is admitted to chamber I5 to force diaphragm I4 and piston I6' towards the left to follow piston 8. Thus at this stage hy- After the operator releases pedal 2, the pressure in chamber 45 is relieved, causing pistons 8 and Sl to yield so that air valves 2| and 2| close and then vacuum valves 29 and 2B open to equalize the pressures in chambers I5 and I6, and I5 and l5. Due tc the existing pressure in chamber 33' the pistons of the high pressure booster return to the starting position. The pistons of the low pressure booster return due to the force of spring d4, and if the bore of cylinder 6 is slightly larger than that of cylinder 5 some assistance is gained from the hydraulic pressure existent in chamber 33. During this retractile movement hydraulic fluid must flow from chamber 45 through hole 3S into chamber 33, unseating ball 3B. When the pistons of both boosters have reached the released, or starting position, rod 33 forces balls 36 and 35 apart so that hydraulic fluid still under pressure in the wheel cylinders may flow through chamber 33', hole 38', and chamber 45 back to the master cylinder.

I claim:

l. In a hydraulic braking system having wheel cylinders to actuate the brakes, a master cylinder, a power operated low pressure booster connested to said master cylinder to receive fluid therefrom and having means to transmit iluid under higher pressure to said wheel cylinders, a power operated high pressure booster connected to said master cylinder to receive fluid therefrom and having means to transmit fluid under higher pressure to said wheel cylinders, a control device for each of said boosters operable by fluid displaced from said master cylinder, and s0 constructed and arranged that operation of said low pressure booster occurs prior to operation of said high pressure booster, and a check valve intermediate said wheel cylinders and said low pressure booster to prevent the return of fluid from the former to the latter.

2. In a hydraulic braking system having wheel cylinders to actuate the brakes, a master cylinder, a power operated low pressure booster connected to said master cylinder to receive fluid therefrom and having means to transmit fluid under higher pressure to said wheel cylinders, a power operated high pressure booster connected to said master cylinder to receive fluid therefrom and having means to transmit fluid under higher presmaster cylinder when said boosters are released.

3. In a hydraulic braking system having wheel cylinders to actuate the brakes, a master cylinder, a low pressure booster connected to said master cylinder to receive duid therefrom, a motor mechanism to operate said low pressure booster, a high pressure booster connected to said master cylinder to receive iiuid therefrom, a motor mechanism to operate said high pressure booster, iiuid transmitting means connecting both of said boosters to said wheel cylinders, a control device for each of said motor mechanisms subject to operation by uid displaced from said master cylinder and so constructed and arranged that operation of the motor mechanism of Said low pressure booster occurs prior to operation of the other motor mechanism, check valve means to prevent the ow of fluid from said high pressure booster to said low pressure booster, and means for returning uid from said wheel cylinders to said master cylinder when said boosters are released.

4. In a hydraulic braking system having wheel cylinders to actuate the brakes, a master cylinder, a low pressure booster, a motor mechanism to operate said low pressure booster, a high pressure booster, a motor mechanism to operate said high pressure booster, a control device for each motor mechanism connected to the master cyl.- inder to be operated by fluid therefrom, and fluid transmitting means connecting both of said boosters to said wheel cylinders, the motor mechanism of said low pressure booster being relatively small to produce relatively limited pressures in said wheel cylinders, said high pressure booster being proportioned to transmit to the wheel cylinders a volume of iiuid which is small relative to the power capacity of its Vmotor mechanism to produce a maximum pressure in said Wheel cylinders, the control device for the motor mechanism of said low pressure booster being constructed to operate iirst to energize such motor mechanism when master cylinder pressures are relatively low, the control device for the motor mechanism of said high pressure booster being adapted to operate to energize the latter motor mechanism when the master cylinder pressures are increased.

5. In a hydraulic braking system having wheel cylinders to actuate the brakes, a master cylinder, a booster unit comprising a high pressure mechanismv and a low pressure mechanism, said booster unit having a control chamber connected to said master cylinder, each such mechanism comprising a pressure chamber and a motor device for reducing the capacities or said chamber, the motor device of said low pressure mechanism being of smaller capacity than the other InOtol mechanism, means connecting said pressure chambers to the wheel cylinders, and a control means for each motor device, each control means being operable by iluid displaced into said control chamber from said master cylinder, said control means for the motor device of said low pressure mechanism being operable by a lower mastei1 cylinder pressure than the control means for energizing the motor device of said high pressure mechanism.

6. Apparatus constructed in accordance with claim 5 wherein each booster mechanism is provided with a check valve providing for the iiow of iiuid from said control chamber to the wheel cylinders, and common means for opening said check valves `when said motor devices are in their ori" positions.

'7. In a hydraulic braking system having wheel cylinders to actuate the brakes, a master cylinder, a booster unit comprising a pair of booster mechanisms, said booster unit having a control charnber communicating with said master cylinder, each booster mechanism having a control piston subject to movement by fluid entering said control chamber, each booster mechanism further comprising a motor device having a power movable unit including a pressure piston, a pressure cylinder in which each of said pressure pistons operates, means connecting said pressure cylinders to said Wheel cylinders, and a control device for each motor device operable by the associated control piston, the control device for the motor device of said low pressure mechanism being operable by a lower master cylinder pressure than the other control device.

8. Apparatus constructed in accordance with claim '7 provided with a check valve preventing the flow of fluid from the wheel cylinders into the pressure cylinder of said low pressure mechanism, each control piston projecting axially through the associated pressure piston to displace :duid from the associated pressure cylinder.

9. Apparatus constructed in accordance with claim 7 wherein said control pistons are in axial alignment and each is provided with an axial passage communicating between said control chamber and the pressure cylinder of the associated mechanism, a check valve for the passage of each control piston opening away from said control chamber, and common means for opening said check valves when said control pistons are in their ofi positions.

WILLIAM STELZER. 

